Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

I need help adjusting transmitt frq of a "coiless fm bug"

Status
Not open for further replies.

Ohm8

New Member
I have this really nifty no coil - no trimmer fm mic that i built from the somewhere on the web. It works great but, the circuit can only transmitt on a fixed frq. The transmitter works on 3 main components and a few others. They are IC-CD4069, BB109 varicap diode and a 10.7mhz ceramic xtal. PLEASE HELP. Can i maybe bias the diode. Many thanks. If u wish to view it the address is https://www.electronic-circuits-diagrams.com/radioimages/radiockt8.shtml
 
I would think you can very the freq. by loading the xtal with a parallel capacitor. A series coil would also bend the freq., no?
Adding a tuned circuit at the antenna would clean up the output some.

Edit: It's not a crystal actually but a filter but it might still be bendable. You might try to replace the filter with a crystal.
 
Last edited:
I've seen that before.

I agree with Nigel, it's a very poor design because it will transmit at every multiple of 10.7MHz up to a couple of hundred 100MHz.

If you're going to add coils then why not just build a properly designed FM transmitter with coils?
 
Last edited:
Or at least add another transistor stage with a tank circuit tuned to 96.3 Mhz. That way you'd get more range with very little frequency drift and it wouldn't be spraying all over the spectrum.
 
It transmits on maybe fifteen different frequencies at the same time, is this not enough? :D
 
All I can see on that page is a big ad that covers the content.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top